This invention relates to radiation emission devices in general, and in particular to radiation emission devices of the type which are frequently referred to as lasers. Lasers are generally characterized by an elongated envelope containing a material which can be raised from an initial energy state to a so-called excited energy state. The particular means used to excite the material in the envelope may vary. Thus, depending on the type of laser used, optical, electrical or chemical excitation means may be employed.
After excitation, radiation may be emitted spontaneously as the excited material returns to a more stable energy level, and/or through stimulated emission. In either case, the wavelength of the radiation so emitted is proportional to the energy difference between the energy levels of the transition involved. This, in turn, depends upon the inherent characteristics of the material itself.
The radiation, which propagates at a constant wavelength, generally leaves the envelope via radiation transmission means disposed at both ends thereof. The radiation transmission means are typically translucent windows which are often, but not necessarily, inclined at an angle which optimizes a particular polarization of light. This inclination is usually referred to as Brewster's angle, and the windows so inclined are often characterized as Brewster's windows.
Lasers of the type described typically include reflection means such as concave mirrors located a predetermined distance beyond each translucent window. The mirrors are aligned such that the radiation emitted from a translucent window is reflected back into the envelope to stimulate the emission of a substantially increased amount of radiation which then passes through the opposite window. This increased radiation is likewise reflected back into the envelope by the other mirror, thereby increasing the emitted radiation even more. As the radiation is continuously reflected back and forth through the envelope, greater and greater amounts of radiation are produced. It is in this manner that the energy of stimulated emission of radiation is "amplified" by the laser device. Of course, in order to enable the amplified radiation to escape therefrom, at least one of the mirrors are generally made only partially reflective.
Many different materials may be used to effect radiation emission, including certain members of the class of materials known as metals. Because the metals used in this type of laser must generally be transformed from a normally solid or liquid state, to a gaseous state in order to effect excitation, such lasers are frequently referred to as metal vapor lasers. It is thus clear that in metal vapor lasers, excitation means must be provided which first vaporize the metal and then raise the vaporized metal from an initial energy state to an excited energy state.
Though metal vapor lasers of the type described have been used to emit radiation, it is well known that they can be subject to certain drawbacks. In particular, the vaporized metal tends to condense on the translucent windows located at the ends of the elongated envelope, thereby rendering the windows relatively opaque, and hence less capable of transmitting radiation. In the past, attempts to remedy this problem have included the use of cataphoretic means for establishing an electric field within the laser envelope. The electric field is typically arranged to accelerate the vaporized metal ion away from the region nearest the translucent windows, thereby confining the vaporized metal to the more central portions of the envelope.
Metal vapor lasers have heretofore required relatively complicated, cumbersome, and inefficient apparatus to accomplish both excitation and confinement of the metal. It is therefore an object of this invention to provide an improved laser configuration which achieves these results more economically and more effectively. It is another object of this invention to provide an improved metal vapor laser characterized by increased laser life and better performance. Other objects, features and advantages of the invention, as summarized below, will be apparent upon reading the following detailed description in conjunction with the accompanying drawings.